Chromium plating



y 1933- E. M. JONES 1,918,605

CHROMIUM PLATING Filed Jan. 9. 1928 6 Sheets-Sheet 1 B6 B 36 BB B0 B0383 O a fi 11 IHIH 3 13 13 B6 141 14 11 I, 64 1 40 s 50' E 47 46 E L i J 10 g'nm'ntoz 09 2 Elmer" mdones July 18, 1933. E. M. JONES CHROMIUM FLA-TING Filed Jan. 9, 1928 6 Sheets-Sheet 2 gwomtow filmer m.dones.

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y 1933- I E. M. JONES 1,918,605

CHROMIUM PLATING Filed Jan. 9, 1928 6 Sheets-Sheet 6 E5 110 2 111 Fig.1) 1 BE 5 0 Q gwwntoc Patented July 18, 1933 UNITED STATES PATENT OFFICE ME I. JONES, O1 DETROIT, MICHIGAN, ASSIGNOR TO PARKER BUST-P3001 00! rm, 0] DETROIT, MICHIGAN,

A CORPORATION 01' MICHIGAN CHBOMIUM PLATING Application filed January 9. 1928. Serial No. 245,594.

This invention relates to chromium plating, and has for its object to improve the methods and apparatus customarily em.- plo ed.

C hromium plating has been accomplished by means of various electrolytes, the one most commonly used being a. solution of chromic oxid, or chromic acid, with a small amount of sulphuric acid. This invention does not have to deal with the composition of the electrolyte, and many variations in the composition may be made without affecting the principles of this invention. However it may be stated that one composition of electrolyte which has been found suitable for use in connection with the invention disclosed in this application is formed by dissolving 300 grams of chromic oxid in a liter ofgater, with 1 cc. concentrated sulphuric ac1 Plating with chromium is more difiicult than with many other metals because chromium plating requires a comparatively high concentration of current and the range of concentration within which a substantially uniform and satisfactory coating can be deposited is limited. The electrolyte used is of comparatively high resistance, and variations in distance of different portions of the cathode from the anode make it ditlicult to produce sufiicient concentration of current on the more distance portions without producing undue concentration on less distant portions. As a result it is difficult to plate articles uniformly, especially when they are of irregular shapes.

In an electrolyte of the kind described, the chromium is normally bound up in negative radicals which tend to travel towards the anode. The positive metallic chromium atom is freed adjacent the cathode, and may be deposited on the cathode. However, unless this metallic atom is protected by the hydrogen until deposited, it recombines in a negative radical and is repelled from the cathode.

This invention has for its purpose to avoid driving the negative radicals carrying chromium awa from the cathode and there by depleting tile supply of chromium within effective range of the plating action on the cathode.

Various ways in which the object of the invention may be at least partially efl'ected will be described in connection with the accompanying drawings, which form a part of this specification.

In the drawings, Figure 1 is a vertical section through one form of apparatus embodying certain features of this invention; Fig. 2 is a horizontal section on the irregular line 22 of Fig. 1; Fig. 3 is a partial section on the line 33 of Fi 4, and is similar to Fig. 1, but shows a di erent form of apparatus; Fig. 4 is a sectional plan on the line 4-4 of Fig. 3; Fig. 5 is a diagrammatic plan view showing successive positions of the anode shown in Figs. 3 and 4; Fi 6 is a perspective view of another form 0 apparatus embodying certain features of the invention; Figs. 7 and 8 are perspective views of forms of apparatus wherein the electrolyte adjacent the cathode is confined by a porous diaphragm; Fig. 9 is a diagrammatic illustration of electrical connections by which various modifications of the current, coming within the range of this invention, may be effected; Fig. 10 is a view combining features of Figs. 3, 7 and 9.

Referring first to the form of apparatus shown in Figs. 1 and 2, there is shown a container 10 within which the electrolyte is placed. For purposes of illustration the electrolyte is not indicated, but it will be readily understood that it will occupy the container beneath the vent opening 11. Vent opening 11 is connected with any desired means for preventing the escape of injurious fumes from the electrolyte where those fumes will be detrimental.

Container 10 is provided with a cover 12 in which there is a series of circular openings 13. In each opening there is a collar 14 having a toothed flange 15, which may be supported upon the cover by means of a bearing 16. In the construction shown the sleeve at the right is shown connected by gearing 17 with the worm 18 of a motor 19, so that the sleeve is continuously rotated. The other sleevu are driven from the sleeve at the right by means of pinions 20.

Above the opening in each sleeve 14 there is mounted a supporting plate 21 which is connected by means of rods 22 with any suitable means for and lowering the same. A rod 23 is fixed in position in plate 21 so that its downward extension is axial of the sleeve 14 therebeneath. In the construction shown the lower end of rod 23 is provided with a hook 24 for supporting the work to be plated, while the upper end of the rod is provided with an electric connection 25.

Attached to the rod 23 there a collar 26 which may be fastened in adjusted position at a desired distance below plate 21 by means of a set screw 27. The u per end of collar 26 provides a bearing 28 or an anode carrier 29. This anode carrier is provided with a central portion 30 adapted to fit rotatably within sleeve 14, and has a flange 31 overlying flange 15 of sleeve 14. Pins 32 project downward from flange 31 and are adapted to enter sockets 33 in flange 15. A conductor plate 34 is attached to the upper face of flange 31, and a contact member 35 is attached to plate 21 in position to contact the rim of plate 34. Contact 35 has an electrical connection 36.

An anode support 37 is pivoted at 38 to plate 35, and its free end 39 is adapted to support an anode 40 which extends downward through an opening 41 in carrier 29. A cam member 42 is fixed u n rod 23. Cam roller 43 is provided on e end 39 of the anode carrier, and a spring 44 normally keeps the roller in contact with cam 42.

Before describing other apparatus for carrying out the invention, the operation of the device shown in Figs. 1 and 2 will be described briefly.

The plate 21 shown at the ri ht of Fig. 1 is indicated as being partial y elevated. It will be understood that when fully elevated hook 24 is above thecover of the tank so that an article 45 may be attached thereto. Thereafter the support 21 is lowered until pins 32 enter sockets 33, whereupon carrier 29 immediately begins rotation with sleeve 14. It will be seen that the electrical connection is established as soon as members 40 and 45 enter the electrolyte. This is desirable as the chromium electrolyte, especially if composed chiefiy of chromic acid, attacks the metal of article 45 very rapidly if it is exposed to the electrolyte without current passing therethrough. However, if the full quantity of current is passed through the electrolyte immediately when a comparatively small portion of the cathode is immersed, there is too great concentration of current, resulting in burning. In the construction shown, the gradual immersion of the anode acts to gradually increase the quantity of the current;

but the gradation of the current to correndtotheincreaseintheimmersedsurface of the cathode during its introduction into the electrolyte may be aided, or entirely taken gate of, by a rheostat or similar control, if

As the carrier 29 rotates it carries anode 40 around the work 45, which remains stationary. The result of this revolution of the anode about the cathode is that the direction of the current is constantly changing. The action of the current adjacent any one portion of the surface of the artcle 45 does not remain constantly in the same direction for any great length of time, and, therefore, the force of the current is not expended in drawing the negative radicals carrying chromium awa from the surface of the cathode. The resu t is, more effective and satisfactory plating than occurs where the current continues to pass in substantially the same direction through the electrolyte. Rotation of the catho e upon its own axis has a tendency to create a current in the electrolyte and thereby accomplish to some degree the same effect, but the revolution of the anode about the cathode is much more effective. The rate of revolution of the anode may be varied to a considerable extent, but a complete revolution once a minute has been found effective for some purposes.

Bg suspending the anode from carrier 37 in t e manner described, the position of the anode relatively to the cathode is controlled by cam 42, so that irregularly shaped articles may be plated more evenly than would be possible with the anode following a fixed circular path. Even if it is found feasible and desirable to. employ an electrolyte in which the chromium atom is normally a free ion, this comparative uniformity of distance between the surfaces of the anode and cathode is desirable for the purpose of obtaining uniformity in both quality and thickness of the resultant coating.

When the form of article 46 shown in the middle of Fig. 1 is to be plated, a straight cathode 40 may be employed, and for an article 47 shown at the left of Fig. 1 an anode 40" ma be employed.

The orm shown in Figs. 3, 4 and 5 is similar to that shown in Figs. 1 and 2, except that provision is made for revolving the anode without rotation thereof about its own axis. This might be accomplished in various ways, 39 but the construction shown therefor in Figs.

3, 4 and 5 is simple and effective.

In this construction there is a fixed gear 48 about the axis of the workholder 49. The anode 50 is carried by a rod 51 to the upper end of which there is attached a gear 52. A late 53 carries rod 51, and is in turn carried y a sleeve 54 depending from a gear 54' rotatable about the axis of the workholder by a motor 57. An idler gear 55 con- I earth Since gears 48 and Teams ff.

d r, rotation of arm 52 about gear 48 'pon its own axis.

of F g.0 av real --passing through the axis ofthe w; iihbld ,ndof the anode support cuts t-li es of the anode and cathode'fal on ychanging lines, so

10 thateachv'e rtic'sfl he of 'the anode may be shapcdas best sui td maintain a substantially the line along the surface ofth dat 'hich it most nearly ill be seen that the is shaped so that I z I y constant distance from the 58 of cathode 59. Likewise thefihjjlift of the anode 60 is shaped ine? L siilistantially constant distanc cathode f nd line 61 of the on the left of the 1's' that this method vihg the anode has iii'g a uniform dis efcathode with cervn in Fig. 1, an operating means simr ears'52, and 58 may and cam it dethe movement of shown in Figs. 3, t shown in Figs. 1 and 2, and, thereterefruru tr description of its operation is unneces a'i'y Fig. 6 there is a trolyte 63 in which fode 64 to be plated, fng the casing for an casing is shown rod 65 re located, and the which passes over lthough contact h to encounter one [leaving the conparking is reduced v 4 current is avoided. N provided, whereby taken from adyof supply, may be leading to the work ading to arm 68. iirstood that a greater than shown in that means may [1 g g n reciprocating these igh a" gwlngs being intendy diagrammatic. The result of I F. r an des i 65 ed to be mrh n by a consideration connecting the various anodes in succession is substantially the same, so far as the plating operation is concerned, as is the revolution of the anode about the work, and is more easily eifected with some forms of work.

It has been found advisable to use the work as an anode temporarily before starting the plating operation, and for this reason the reversing switch has been shown. It is also advisable, under some circumstances, to use the reversing switch temporarily during the plating operation, as will be more fully explained later.

In Fig. 7 there is shown a. diagrammatic illustration of a container of an electrolyte '76 in which there is hung a cathode 77 and an anode T8. In this device the cathode and anode are indicated as remaining stationary, but a diaphragm or container 79 is shown about the cathode. This container may be of porous earthenware or similar material which may not interrupt the electric current, but will segregate the electrolyte immediately adjacent the cathode from the liquid in the other portion of the container. In this way the limit of the travel of the negative radicals carrying chromium is fixed by the container 79, and, therefore, these chromiun1-bearing radicals are maintained more closely in the vicinity of the work than would be possible if they were at liberty to travel to the anode 78.

Figure 8 is similar in general principle to Fig. 7, except that itshows the partition 80 between anode 81 and cathode 82 in the form 1 of a diaphragm extending completely across the tank instead of a receptacle surrounding the work. In addition there is shown the reversing switch 83;

Regardless of whether diaphragm 80 is used or not, reversing switch 83 may be employed for limiting the travel of the negative radicals away from the cathode. If the current is momentarily reversed, it will be readily understood that the negative radicals 11 will be drawn towards the cathode, and when the current is again applied in the usual direction there will be a chromium supply adjacent the cathode ready for the operation. A short reversal of the direction of the current during the plating operation at suitable intervals is therefore desirable.

Figure 9 shows apparatus for taking further advantage of changes in current to accomplish similar results to those accomplished by the apparatus shown in Figs. 1 to 5. In Fig. 9 there is shown a container 84 for an electrolyte 85 in which there are immersed a cathode 86 and anode 87. It will be understood that these are merely diagram- I matically illustrated in the figure, as are also the electric connections.

There are shown lead lines 88 and 89 leading from the cathode and anode, respectively, to a switch 90 which connectswith a direct current dynamo 91 through a suitable variable resistance 92.

Branch lines 93 and94 lead from lines 88 and 89, respectively, to a switch 95 which connects them wi lead lines 96 and 97, respectively. Line 96 is connected through a suitable variable resistance 98 with a transformer 99 energized from an alternating current dynamo 100. The other lead line 101 1 from transformer 99 is provided with branches 102 and 103. Branch 102 leads to a terminal 104 which may be connected by a switch 105 with line 97. Branch 103 connects through an asymmetric cell 106 with a terminal 107, which also may be connected by switch 105 with lead line 97 A by-pass 108 is provided past cell 106 through a variable resistance 109.

- It will be readily understood that switch 95 I may be opened and the plating operation performed in the usual manner by closing switch 90.- If desired, both may be closed and switch 105 moved to connect terminal 104 with line 97, whereupon alternating current from d amo 100 will be superimposed upon the direct current from d amo 91. The character of the resulting current will depend upon the relative intensity of the currents of the two sources. If the maximum of the current from dynamo 100 exactly equalled the current from dynamo 91, the resultant flow through the electrolyte would consist of a current va ing from zero to twice the intensity of t e current from dynamo 9 1. A

I less intensity of the alternating current would result in a fluctuating constant current, whereas reducing the current from dynamo 91 or increasing that from dynamo 100 would result in an alternating current with one '10 ofilthe phases longer and stronger than the ot er.

Switch 105 may be moved to terminal'107 instead of to terminal 104. Thereupon current passes through asymmetric cell 106 to a .0 variable degree, depending upon the adjustment of resistance 109. By this arrangement an alternating current with onephase longer and stronger than the other may be obtained with switch 90 open, or this arrange- 210 ment could be used in conjunction with the direct current dynamo to obtain the desired strength of the current at different intervals.

The voltage of the-cur'rentmay be cons derably varied under difierent conditions,

I. .68 and, therefore, no exact voltages will be given,

but it may be pointed. out t ages may be used with an intermittent current than with a constant current, and that thevoltage may be still further increased with an alternating current, depending amongst other things, upon the frequency oi the alternation. a V

mreadily understood that the use of an intermittent current is comparable to M the results achieved by the use of such appa- .similar at higher voltratus as shown in Fig. 6, where each anode is energized intermittently. However, it will be noted that electricity is constantly flowing through some anode in the construction shown in Fig. 6, sons to avoid injurious action of the electrolyte upon the work. In. all cases where an intermittent current is; used, the period of absolute cutting oif of the current must be short in order to avoid deleterious results from the action of electrolyte upon the work.

. When the current is alternated, with one phase lon er and stronger than the other, it will be un erstood that the short phase maintains a current through the electrolyte and avoids deleterious action upon the work and at the same time acts to halt the movement of negative radicals away from the work and to move them towards the work. By such an alternating current, negative radicals are brought close to the cathode, and then during the longer and stronger phase of the current these radicals are decomposed by the hydro gen liberated at the cathode and the metallic atoms are deposited upon the work:

While difi'erent methods of retaining metal-carrying negative radicals adjacent the cathode have been illustrated separately, it will be understood that the tons diaphragm of Fi 7 or Fi 8-, an the reversmg switch of ig. 8 or t e electrical connections of Fig. 9 could be employed with the constructions shown in Figs 1 to 6, if desired, the use of the diaphr reversal of the current, and revolution of the efiective anode being capable of use separately or in an desired combination. 7

ig. illustrates one such possible combination. Parts in Fig. 10 corresponding to elements shown in Figs. 3, 7 and 9 are given reference characters to those emloyed in Figs. 3, 7 and 9 and used in the oregoing' description, each character beingi primed ,on'Fi 10. The construction an o ration of e device shown in Fig. 10 is o vious from the foregoing description so far as similar arts have been descri in. connection Figs. 3, 7 and 9; but the electric connections to the anode and cathode are not shown in Fig. 3, and therefore addie tional description of this feature, as shown in Fig. 10, will be 'ven.

The cathode camer49' is arranged ly of a carrier supported by rods 22', similarto rods-22 shown in Fig. 1, and the entire mechanism support' (1 9 rating the cathode and an e may re and lowered by these rods. A lead has electrical connection through member 49' with cathode 58' and leads to a contact 110 which is raised and lowered with rods 22". When rods 22" are lowered so that the cathode begins toenter the bath, contactl-IO makes connection with lead 88' through resistance 111, and as the cathode is lowered deeper into the bath, contact 110 slides down resistance 111, thereby cutting out the resistance proportionately to the dipping of the cathode in the bath, for purposes mentioned above in connection with the description of Fig. 1.

The upper end 112 of rod 51', supporting the anode, makes contact with a conducting ring 113. Ring 113 is insulated except for its contacts with 112 and with a lead 114 connected to a contact 115 which is raised and lowered with rods 22. A resistance member 116 is related to contact 115 and lead 89 in the same way as resistance 111 is related to contact 110 and lead 88.

With the particular shape of cathode 61 shown in Fig. 10, it is desirable to shape the anode 56 as shown in that figure, and carry it so that, in one point of its travel, its lower end projects under the cathode, as shown in its dotted line position in the drawings. This necessitates supporting the cup 79 on a support 117 that is offset so as to provide a free path for the anode. Obviously, the device should not be raised or lowered with the anode in its dotted line posi tion, but with it in its full line position or at one side, so cup 7 9 does not interfere with the vertical movement of the anode.

The constructions shown in Figs. 1 and 2 and in Figs. 3, 4 and 5 show two methods of manipulating the anode, during its revo lution, for the purpose of approximating a constant distance between the adjacent surfaces of the anode and cathode. It will be readily understood that other shapes of articles may render different movements of the anode more useful for the stated purpose. The movements described, or a combination thereof, are useful with a great variety of articles, but other obvious manipulations for the same purpose come within the scope of the broader claims appended hereto.

These manipulations are useful, not only with a chromic acid electrolyte, but also with other electrolytes, such as chromium chloride, etc., for reasons indicated above.

Without a specific enumeration of further modifications, it will be understood that this invention comprises other obvious equivalents of the described constructions and operations which are within the scope of the appended claims.

What I claim is:

1. The process of electro-platmg with an electrolyte containing chromium combined in negative radicals. which comprises immersing an article to be plated in the electrolyte, passing an electric current through the electrolyte, and limiting the travel of the negative radicals away from the article by changing the direction of the effective anode with respect to the position of said radicals before said radicals have travelled more than a limited distance from the anode.

2. The process of electro-plating with an electrolyte containing chromium combined in negative radicals, which comprises immersing an article to be plated in the electrolyte, passing an electric current through the electrolyte, and limiting the travel of the negative radicals away from the article by reversing the current at intervals, the reversed current being maintained for a shorter length of time than the current in the usual direction.

3. The process of electro-plating with an electrolyte containing chromium combined in negative radicals, which comprises immersing an article to be plated in the electrolyte, passing an electric current through the electrolyte, and limiting the travel of the negative radicals away from the article by reversing the current at intervals, the reversed current being of less voltage than the current in the usual direction.

4. The process of electro-plating with an electrolyte containing chromium combined in negative radicals. which comprises immersing an article to be plated in the electrolyte, passing an electric current through the electrolyte, and limiting the travel of. the negative radicals away from the article by alternating the current, the phase of the current with the article as the anode being shorter and Weaker than the phase of the current with the article as the cathode.

5. The method of electro-plating with chromium an article having a surface which is other than one of rotation, which comprises forming an electrolyte containing chromium, mmersing the article in the electrolyte, immersing an anode in the electrolyte, passing a current through the electrolyte using the article as a cathode, revolving the anode about the article, and manipulating the anode during its revolution so as to maintain the adjacent sides of the anode and article at an approximately constant distance apart.

6. The process of electro-plating which comprises forming an electrolyte containing chromic acid, immersing an article to be coated in the electrolyte, passing a current through the electrolyte using the article as a cathode, and revolving the effective anode about the article.

7. The process of electro-plating which 1 comprises forming an electrolyte containing chromic acid, immersing an article to be coated in the electrolyte, passing a current through the electrolyte using the article as a cathode, and reversing the current at intervals, less electro-motive force being employed during the reversal of the current than during the passage of the current with the article as the cathode.

8. The process of electro-plating an article having a surface other than a surface of rotation, which comprises immersing the article in an electrolyte and employing it as a cathode, introducing-an anode into the electrolyte, revolvingthe anode about the article, and synchronously giving the anode a movement other than that of revolution and one which maintains the surface of the anode at substantially constant distance from the surface of the article.

9. Electro-plating apparatus comprising a support for a cathode, a support for an anode, a carrier for the anode support, the carrier being mounted rotabably about the cathode support, meansto rotate the carrier and thereby revolve the anode support about the cathode support, and means to rotate the anode support synchronously with its revolution and in the reverse direction with respect to the carrier.

10. Apparatus for electrolating comprising a container for an. e ectrolyte, an anode, a support for an article to be plated in the electrolyte, means to revolve the anode about the article thus supported, and means to give the anode, during its revolion, a movement in addition to that of revolution to maintain an approximately constant distance between the adjacent surfaces of the anode and article.

11. Apparatus for electro;plating comp a container for an ectrolytc, an anode, a support for an article to be plated 'ing the article suppo means to revolve the anode rted, and combetween the adjacent sur arms of the anode and article, and common means for raising and lowering the article and anode with respect to the container.

13. In electro-plating apparatus, a container for an electrolyte, a cover for the container, an approximately circular opening in the cover, asleeve mounted in said opening, means for constantly the sleeve, an article carrier mounted axi of the sleeve, an anode support, a carrier or the sufport mounted rotatably about the axis 0 said sleeve, common means for raising and lowerrt and said carrier, and means for connecting the carrier with the sleeve to be rotated therewith when the carrier is in lowered position.

' M. JONES.

hm/Imus 

